Portable communication devices such as cellular phones typically have a number of radio frequency (RF) power amplifiers (PAs) in order to be able to handle transmissions on a number of different communication standards (e.g., Wideband Code Division Multiple Access (WCDMA), Global System for Mobile Communications (GSM/EDGE)) and on different communication bands (e.g., low band (800 MHz to 900 MHz), high band (1.8 GHz to 1.9 GHz). Each power ampflifier (PA) may have its own individual value of bias voltage.
In prior art radio frequency (RF) power management circuits, each individual value of bias voltage may be provided by an individual regulator (e.g., low drop out (LDO) regulator) in order to meet specified load requirements. For communication systems that have many different power amplifiers (PAs), this approach will require many different regulators in order to provide the required bias voltages for the power amplifier (PA) biases.
For example, in the Direct Current (DC) to Direct Current (DC) Converter LM3280 manufactured by National Semiconductor Corporation there are three low dropout (LDO) regulators that provide three bias voltages intended for three Wideband Code Division Multiple Access (WCDMA) power amplifiers. This type of architecture is illustrated in FIG. 1.
As shown in FIG. 1, prior art circuit 100 employs three regulators (110, 120, 130). First regulator 110 receives an enable signal EN1 and a reference voltage signal VREF and outputs an output voltage VBIAS1. Second regulator 120 receives an enable signal EN2 and a reference voltage signal VREF and outputs an output voltage VBIAS2. Third regulator 130 receives an enable signal EN3 and a reference voltage signal VREF and outputs an output voltage VBIAS3. The three regulators (110, 120, 130) operate in parallel. Each regulator may comprise a low dropout (LDO) regulator circuit, a charge pump regulator circuit (also known as a switching capacitor regulator circuit), or any similar type of regulator circuit.
In other types of prior art circuits there are two regulators for the low band power amplifiers (PAs) and two regulators for the high band power amplifiers (PAs). There will be a need for an increased number of regulators as cellular phone technology continues to develop. There will be a need to be able to handle more standards and more frequency bands. For example, there are presently ten (10) frequency bands in Wideband Code Division Multiple Access (WCDMA) technology.
One prior art approach to reducing the number of regulators for the power amplifier (PA) bias voltages is to switch the output of a regulator to one specific bias voltage output port and disable the other bias voltage output ports. This approach is illustrated in the circuit 200 shown in FIG. 2. As shown in FIG. 2, one regulator 210 is employed. Regulator 210 separately receives three enable signals (EN1 and EN2 and EN3) on a first input. Regulator 210 receives a reference voltage signal VREF on a second input. Regulator 210 also receives a feedback signal (FB) on a third input.
In response to receiving one of the enable signals (e.g., EN1), regulator 210 outputs to a demultiplexer circuit 220 a regulator voltage VREG that is associated with the received enable signal. The feedback signal (FB) that is provided to the third input of regulator 210 is from a common internal node (VREG) taken at the output of the regulator 210.
Demultiplexer circuit 220 also separately receives the three enable signals (EN1 and EN2 and EN3) on a selector input. When the demultiplexer circuit 220 receives the first enable signal EN1, the demultiplexer circuit 220 outputs the regulator voltage signal VREG that is associated with the first enable signal EN1 on the first bias voltage output port as VBIAS1. The other two bias voltage output ports (VBIAS2 and VBIAS3) are disabled.
When the demultiplexer circuit 220 receives the second enable signal EN2, the demultiplexer circuit 220 outputs the regulator voltage signal VREG that is associated with the second enable signal EN2 on the second bias voltage output port as VBIAS2. The other two bias voltage output ports (VBIAS1 and VBIAS3) are disabled. Similarly, when the demultiplexer circuit 220 receives the third enable signal EN3, the demultiplexer circuit 220 outputs the regulator voltage signal VREG that is associated with the third enable signal EN3 on the bias voltage output port as VBIAS3. The other two bias voltage output ports (VBIAS1 and VBIAS2) are disabled.
This prior art approach has several problems. First, all of the power amplifiers (PAs) have to have similar steady state levels. Second, there will be differences at the bias voltage outputs due to loading differences. Third, each bias voltage output will have process, temperature and supply variations due to switch resistance variations.
Therefore, there is a need in the art for a system and method that is capable of solving the problems that occur in the prior art. In particular, there is a need in the art for a system and method for efficiently controlling a regulator circuit for multi-band radio frequency (RF) power amplifier (PA) biases.
The system and method of the present invention solve the problems that are associated with the prior art by controlling the regulator circuit with a feedback loop that is connected to the plurality of the bias voltages that are output from the regulator circuit. The feedback loop comprises a demultiplexer circuit and a multiplexer circuit that each receive an enable signal and provide a feedback signal to the regulator circuit from the bias voltage that is associated with the received enable signal. The system and method of the invention allow the regulator circuit to be configured as needed to provide different values of radio frequency power amplifier bias voltages.
Before undertaking the Detailed Description of the Invention below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.
Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior uses, as well as to future uses, of such defined words and phrases.